This application claims the priority of German Application No. 101 21 388.3 filed May 2, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an internal combustion engine and to a method for operating an internal combustion engine having a preparation device for fuel which provides a starting fuel comprising low boiling temperature fuel constituents.
An internal combustion engine in which a distilled fuel which is produced on board is fed to the internal combustion engine in the starting phase and the subsequent warm-up phase is already known (German Patent Document DE 42 15 949 c1). This starting fuel/air mix, which comprises low-boiling constituents, referred to below as the starting fuel, is delivered via a metering valve to the induction pipe of the internal combustion engine downstream of a throttle valve. The use of starting fuel makes it possible for combustion which is as complete as possible to take place in the combustion chambers of the internal combustion engine. However, during the cold start of the internal combustion engine, the catalytic converter has not yet reached its operating temperature and is therefore substantially ineffective, so that, despite the use of starting fuel, in particular when power is demanded from the internal combustion engine during the warming up, uncleaned exhaust gases, such as hydrocarbons (HC) and in particular nitrogen oxides (NOx), can be discharged to the environment. It is therefore desirable for the catalytic converter to reach its operating temperature as quickly as possible.
Furthermore, German Patent Document DE 40 41 628 A1, corresponds to U.S. Pat. No. 5,205,120 has disclosed the blowing in of secondary air, the engine being operated with excess fuel during the time in which the secondary air is being blown in. The hydrocarbons (HC) which are formed in the exhaust gas as a result of the excess of fuel are then oxidized by means of secondary air, which is introduced into the exhaust train, in an afterburning step carried out in the catalytic converter, with heat being generated. During the cold-start phase of the internal combustion engine, this heat leads to the catalytic converter being heated as quickly as possible, in order, in this way, to obtain an accelerated response of the catalytic converter. However, despite this measure, it is impossible to avoid a considerable proportion of hydrocarbons (HC) and in particular of nitrogen oxides (NOx) being present in the exhaust gas.
The internal combustion engine according to the invention and the method according to the invention for operating the internal combustion engine utilize a secondary device provided for after-treatment of the exhaust gases in which air is blown into the exhaust train upstream of the catalytic converter, the combustion being carried out with an excess of starting fuel (rich-burn operation) during the cold start and the subsequent warm-up phase. The preferred embodiments of the invention have the advantage over prior systems in that the levels of emissions of harmful constituents in the exhaust gas from the internal combustion engine during the cold start and the subsequent warm-up phase of the internal combustion engine are lowered further, with the result that future stringent SULEV (super ultra low emission vehicles) exhaust limits can be complied with easily. It is particularly advantageous according to certain preferred embodiments of the invention that the catalytic converter is heated up particularly rapidly during the cold start. A further advantage of preferred embodiments is that predetermined exhaust limits for a prescribed test cycle, which requires power to be delivered from the internal combustion engine after a certain idling phase of the internal combustion engine in the warm-up phase, can be complied with.
The measures described herein and in the claims allow advantageous refinements and improvements to an internal combustion engine and the method for operating an internal combustion engine according to preferred embodiments of the present invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.